Molten metal pump rotor

ABSTRACT

A molten metal pumping device is disclosed that comprises a pump base including at least one input port, a pump chamber, a chamber wall, and a discharge leading to an output port. A rotor is retained within the chamber and is connected to a rotor shaft. The rotor is a dual-flow (or mixed-flow) rotor, directing molten metal both into the chamber and out of the chamber, where it ultimately exits through the discharge. The dual-flow rotor has a recess to permit high amounts of molten metal to enter the pump chamber.

This application claims priority to U.S. Provisional Application No.61/247,509 entitled “Molten Metal Pump Rotor” which was invented by PaulV. Cooper and filed on Sep. 30, 2009. U.S. application Ser. No.12/853,238 entitled “Quick Submergence Molten metal Pump,” filed on Aug.9, 2010 is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to novel impellers that may be used in variousdevices, particularly pumps for pumping molten metal, and devicesincluding the impellers (also called “rotors”).

BACKGROUND OF THE INVENTION

As used herein, the term “molten metal” means any metal or combinationof metals in liquid form, such as aluminum, copper, iron, zinc, andalloys thereof. The term “gas” means any gas or combination of gases,including argon, nitrogen, chlorine, fluorine, Freon, and helium, whichmay be released into molten metal.

A reverbatory furnace is used to melt metal and retain the molten metalwhile the metal is in a molten state. The molten metal in the furnace issometimes called the molten metal bath. Reverbatory furnaces usuallyinclude a chamber for retaining a molten metal pump and that chamber issometimes referred to as the pump well.

Known pumps for pumping molten metal (also called “molten-metal pumps”)include a pump base (also called a “base,” “housing” or “casing”) and apump chamber (or “chamber” or “molten metal pump chamber”), which is anopen area formed within the pump base. Such pumps also include one ormore inlets in the pump base, an inlet being an opening to allow moltenmetal to enter the pump chamber.

A discharge is formed in the pump base and is a channel or conduit thatcommunicates with the molten metal pump chamber, and leads from the pumpchamber to the molten metal bath. A tangential discharge is a dischargeformed at a tangent to the pump chamber. The discharge may also beaxial, in which case the pump is called an axial pump. In an axial pumpthe pump chamber and discharge may be the essentially the same structure(or different areas of the same structure) since the molten metalentering the chamber is expelled directly through (usually directlyabove or below) the chamber.

A rotor, also called an impeller, is mounted in the pump chamber and isconnected to a drive shaft. The drive shaft is typically a motor shaftcoupled to a rotor shaft, wherein the motor shaft has two ends, one endbeing connected to a motor and the other end being coupled to the rotorshaft. The rotor shaft also has two ends, wherein one end is coupled tothe motor shaft and the other end is connected to the rotor. Often, therotor shaft is comprised of graphite, the motor shaft is comprised ofsteel, and the two are coupled by a coupling, which is usually comprisedof steel.

As the motor turns the drive shaft, the drive shaft turns the rotor andthe rotor pushes molten metal out of the pump chamber, through thedischarge, which may be an axial or tangential discharge, and into themolten metal bath. Most molten metal pumps are gravity fed, whereingravity forces molten metal through the inlet and into the pump chamberas the rotor pushes molten metal out of the pump chamber.

Molten metal pump casings and rotors usually, but not necessarily,employ a bearing system comprising ceramic rings wherein there are oneor more rings on the rotor that align with rings in the pump chambersuch as rings at the inlet (which is usually the opening in the housingat the top of the pump chamber and/or bottom of the pump chamber) whenthe rotor is placed in the pump chamber. The purpose of the bearingsystem is to reduce damage to the soft, graphite components,particularly the rotor and pump chamber wall, during pump operation. Aknown bearing system is described in U.S. Pat. No. 5,203,681 to Cooper,the disclosure of which is incorporated herein by reference. U.S. Pat.Nos. 5,951,243 and 6,093,000, each to Cooper, the disclosures of whichare incorporated herein by reference, disclose, respectively, bearingsthat may be used with molten metal pumps and rigid coupling designs anda monolithic rotor. U.S. Pat. No. 2,948,524 to Sweeney et al., U.S. Pat.No. 4,169,584 to Mangalick, and U.S. Pat. No. 6,123,523 to Cooper (thedisclosure of the afore-mentioned patent to Cooper is incorporatedherein by reference) also disclose molten metal pump designs. U.S. Pat.No. 6,303,074 to Cooper, which is incorporated herein by reference,discloses a dual-flow rotor, wherein the rotor has at least one surfacethat pushes molten metal into the pump chamber.

The materials forming the molten metal pump components that contact themolten metal bath should remain relatively stable in the bath.Structural refractory materials, such as graphite or ceramics, that areresistant to disintegration by corrosive attack from the molten metalmay be used. As used herein “ceramics” or “ceramic” refers to anyoxidized metal (including silicon) or carbon-based material, excludinggraphite, capable of being used in the environment of a molten metalbath. “Graphite” means any type of graphite, whether or not chemicallytreated. Graphite is particularly suitable for being formed into pumpcomponents because it is (a) soft and relatively easy to machine, (b)not as brittle as ceramics and less prone to breakage, and (c) lessexpensive than ceramics.

Three basic types of pumps for pumping molten metal, such as moltenaluminum, are utilized: circulation pumps, transfer pumps andgas-release pumps. Circulation pumps are used to circulate the moltenmetal within a bath, thereby generally equalizing the temperature of themolten metal. Most often, circulation pumps are used in a reverbatoryfurnace having an external well. The well is usually an extension of acharging well where scrap metal is charged (i.e., added).

Transfer pumps are generally used to transfer molten metal from theexternal well of a reverbatory furnace to a different location such as alaunder, ladle, or another furnace. Examples of transfer pumps aredisclosed in U.S. Pat. No. 6,345,964 B1 to Cooper, the disclosure ofwhich is incorporated herein by reference, and U.S. Pat. No. 5,203,681.

Gas-release pumps, such as gas-injection pumps, circulate molten metalwhile releasing a gas into the molten metal. In the purification ofmolten metals, particularly aluminum, it is frequently desired to removedissolved gases such as hydrogen, or dissolved metals, such asmagnesium, from the molten metal. As is known by those skilled in theart, the removing of dissolved gas is known as “degassing” while theremoval of magnesium is known as “demagging.” Gas-release pumps may beused for either of these purposes or for any other application for whichit is desirable to introduce gas into molten metal. Gas-release pumpsgenerally include a gas-transfer conduit having a first end that isconnected to a gas source and a second submerged in the molten metalbath. Gas is introduced into the first end of the gas-transfer conduitand is released from the second end into the molten metal. The gas maybe released downstream of the pump chamber into either the pumpdischarge or a metal-transfer conduit extending from the discharge, orinto a stream of molten metal exiting either the discharge or themetal-transfer conduit. Alternatively, gas may be released into the pumpchamber or upstream of the pump chamber at a position where it entersthe pump chamber. A system for releasing gas into a pump chamber isdisclosed in U.S. Pat. No. 6,123,523 to Cooper. Furthermore, gas may bereleased into a stream of molten metal passing through a discharge ormetal-transfer conduit wherein the position of a gas-release opening inthe metal-transfer conduit enables pressure from the molten metal streamto assist in drawing gas into the molten metal stream. Such a structureand method is disclosed in U.S. application Ser. No. 10/773,101 entitled“System for Releasing Gas into Molten Metal”, invented by Paul V.Cooper, and filed on Feb. 4, 2004, the disclosure of which isincorporated herein by reference.

Generally, a degasser (also called a rotary degasser) is used to removegaseous impurities from molten metal. A degasser typically includes (1)an impeller shaft having a first end, a second end and a passage (orconduit) therethrough for transferring gas, (2) an impeller (also calleda rotor), and (3) a drive source (which is typically a motor, such as apneumatic motor) for rotating the impeller shaft and the impeller. Thedegasser impeller shaft is normally part of a drive shaft that includesthe impeller shaft, a motor shaft and a coupling that couples the twoshafts together. Gas is introduced into the motor shaft through a rotaryunion. Thus, the first end of the impeller shaft is connected to thedrive source and to a gas source (preferably indirectly via the couplingand motor shaft). The second end of the impeller shaft is connected tothe impeller, usually by a threaded connection. The gas is released fromthe end of the impeller shaft submersed in the molten metal bath, whereit escapes under the impeller. Examples of rotary degassers aredisclosed in U.S. Pat. No. 4,898,367 entitled “Dispersing Gas IntoMolten Metal,” U.S. Pat. No. 5,678,807 entitled “Rotary Degassers,” andU.S. Pat. No. 6,689,310 to Cooper entitled “Molten Metal DegassingDevice and Impellers Therefore,” the respective disclosures of which areincorporated herein by reference.

SUMMARY OF THE INVENTION

The invention relates to rotors that can be used in molten metaldevices, such as molten metal pumps, and to devices that include therotors. A rotor according to the invention is dual-flow (or mixed-flow)meaning that it both directs (or pushes) molten metal into the pumpchamber as it rotates, and directs (or pushes) the molten metal out ofthe pump chamber as it rotates. A rotor according to the invention hasone or more vanes wherein each vane has a leading edge to direct moltenmetal into the pump chamber and a surface beneath the leading edge todirect molten metal out of the chamber. The leading edge preferablyincludes a downwardly-curved surface (also called a first surface) andthe surface that directs molten metal outward (also called a secondsurface) preferably has a portion that has a downwardly-sloping, angledor curved portion that leads to a curved bottom. Alternatively, thesecond surface may be u-shaped or v-shaped or include a u-shaped orv-shaped portion. A rotor according to the invention also preferablyincludes a top surface and a recess formed in the top surface to allowlarge amounts of molten metal to enter the pump chamber. The recess in apreferred embodiment is an angled surface on the top of a vane of therotor followed by a vertical surface that extends to the base of therotor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial, cross-sectional side view of a pump including animpeller according to an aspect of the invention.

FIG. 1 a is a partial, cross-sectional view of a pump casing thatincludes an impeller according to one aspect of the invention.

FIG. 2 is a side view of an impeller according to the invention.

FIG. 3 is a different side view of the impeller of FIG. 2.

FIG. 4 is a perspective side view of the impeller of FIGS. 2 and 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the figures, where the purpose is for describing apreferred embodiment of the invention and not for limiting same, FIG. 1shows a pumping device 10 submerged in a metallic bath B. Device 10 hasa superstructure 20 and a base 50. Superstructure 20 is positionedoutside of bath B when device 10 is operating and generally comprises amounting plate 24 that supports a motor mount 26. A motor 28 is mountedto mount 26. Motor 28 is preferably electric or pneumatic although, asused herein, the term motor refers to any device capable of rotating arotor.

Superstructure 20 is connected to base 50 by one or more support posts30. Preferably posts 30 extend through openings (not shown) in plate 24and are secured by post clamps 32, which are preferably bolted to thetop surface (preferred) or lower surface of plate 24.

A rotor 100 is driven by a drive shaft 12 preferably comprised of amotor drive shaft connected to a rotor drive shaft 40. The motor driveshaft has a first end (not shown) and a second end 36, the first endbeing connected to motor 28. The preferred structure for connecting themotor drive shaft to rotor drive shaft 40 is a coupling 38. Coupling 38has a first coupling member 90 attached to second end 36 of the motordrive shaft, and a second coupling member 180. A rotor shaft 40 has afirst end 42 and a second end 44. First end 42 is connected to secondend 36 of the motor shaft, preferably by coupling 38, by connectingfirst end 42 to second coupling member 180. The motor drive shaft drivescoupling 38 which, in turn, drives rotor shaft 40. Preferably, coupling38 and first end 42 of rotor shaft 40 are connected without the use ofconnecting threads.

Base 50, and all of the components of device 10 exposed to the moltenmetal, are preferably formed from graphite or other material, such asceramic, suitable for use in molten metal. Base 50 includes a topsurface 54 and an input port (or inlet) 56, preferably formed in topsurface 54. Alternatively, an inlet could be formed in the bottomsurface or pump 10 could be a dual-inlet pump with inlets in both topsurface 54 and the bottom surface.

A pump chamber 58, which is in communication with port 56, is a cavityformed within housing 50. Chamber 58 is partially defined by a chamberwall 59. A discharge 60, shown in FIG. 1, is preferably formedtangentially with, and is in fluid communication with, pump chamber 58.Discharge 60 leads to an output port (or outlet) 62 formed in a sidesurface of housing 50. Alternatively, the discharge may be formed in topsurface 54 if the pump were a transfer pump, or the discharge may be thebottom or top opening of the pump chamber if the pump is an axialdischarge pump. Base 50 preferably includes a wear ring (or bearingring) 64 that is preferably made of ceramic and is cemented to the loweredge of chamber 58.

The rotor of the present invention may be used with any type of moltenmetal pump. As shown in FIG. 1, rotor 100 is imperforate, formed ofsolid graphite, is mounted in a circulation pump, is attached to anddriven by shaft 40 and is preferably placed centrally within chamber 58.Referring to FIGS. 2-4, rotor 100 preferably has three vanes 102. Rotor100 may, however, have any number of vanes and be formed of any materialsuitable for use in a molten metal environment.

Rotor 100 further includes a connective portion 104, which is preferablya threaded bore, but can be any structure capable of drivingly engagingrotor shaft 40. It is most preferred that the outer surface of secondend 44 of shaft 40 has tapered threads and bore 104 be threaded toreceive the tapered threads. A flow blocking plate 106 is preferablyformed of ceramic and is cemented to the base 108 of rotor 100, but maybe integrally formed with the rotor 100. In the embodiment shown, plate106 preferably rides against circular bearing ring 64 in pump chamber 58and substantially blocks molten metal from entering or exiting throughthe bottom of chamber 58. Alternatively, plate 106 could be replaced bya plurality of individual bearing pins mounted in the rotor, or thebearing ring could potentially be eliminated. In addition, the rotorcould have a bearing surface integrally formed therein, such a bearingring being either graphite or ceramic. Or, the bearing ring and/orbearing surface could be entirely eliminated, in which case the pumpwould preferably include a shaft or other device to keep the rotorcentered in the pump housing.

The preferred dimensions of rotor 100 will depend upon the size of thepump (because the size of the rotor varies with the size of the pump)and on manufacturer's specifications. The preferred proportions of rotor100, however, are shown in FIGS. 2-4. A rotor according to the inventionshould have a structure that directs flow into the pump chamber and astructure that directs flow out of the pump chamber. This isaccomplished by providing at least one vane on the rotor that bothdirects molten metal into the chamber and out of the chamber.

A vane, as shown, is a solid structure that extends outwardly from thehub of the rotor, and that is spaced apart from the other vanes.Preferably each vane 102 has the same configuration so only one vane 102shall be described. Each vane 102 preferably includes avertically-oriented portion 102A and a substantiallyhorizontally-extending portion 102B. The respective vertical andhorizontal orientation of the portions described herein is in referenceto a rotor positioned in a standard pump having an input port in its topsurface. The invention, however, covers any rotor for use in amolten-metal pump, whether the input port is formed in the top surface,bottom surface or a side surface. It will be therefore understood thatthe terms “horizontal” and “vertical” refer to the rotor when it is inthe orientation shown in the Figures.

In the preferred embodiment, portion 102B (also called a projection orhorizontally-extending projection) is positioned closer to inlet 56 thanportion 102A. This is because the molten metal in bath B outside ofinlet 56 should first be directed into chamber 58 by portion 102B beforebeing directed outward by portion 102A. Projection 102B has a topsurface 112 preferably substantially flush with inlet 56 and a bottomsurface 114. However, surface 112 and projection 102B may be positionedoutside or inside of inlet 56. Projection 102B further includes adownwardly-curved, leading surface (or first surface) 118. As will beunderstood, surface 118 is curved such that, as rotor 100 turns (asshown it turns in a clockwise direction) surface 118 directs moltenmetal into pump chamber 58 (i.e., downward towards plate 106 in theembodiment shown). Any surface that functions to direct molten metalinto chamber 54 can be used, but it is preferred that the downward curveof surface 118 forms a substantially 30 degree-60 degree, and mostpreferably, a 45 degree angle. Surface 118 could also be planar althougha curved surface is preferred. Projection 102B also preferably includesa lip 120. Lip 120 is optional, and prevents too thin an edge from beingformed when surface 118 is cut into projection 102B. This reduces thelikelihood of breakage during shipping or handling of rotor 100, but isnot related to the overall function of rotor 100 during operation ofpump 10.

Portion 102A extends from the back (or trailing portion) of projection102B to base 108. Portion 102A has a surface (the “second surface”) 132that preferably has a downwardly-angled top portion 132A (wherein theangle is preferably between 30 degrees and 60 degrees) and a curvedbottom portion 132B, so that it directs molten metal outward as rotor100 rotates. Angled top portion 132A may be substantially planar (asshown), curved or multi-faceted. Further, surface 132 may be u-shaped orv-shaped, or include a portion that is u-shaped or v-shaped.

A recess 150 is formed in top surface 112 and includes an angled surface134 and a vertical, cut-away portion 134A. As shown, recess 150 beginsat a position on surface 112 slightly forward of face 132. The purposeof recess 150 is to reduce the area of top surface 112, thereby creatinga larger opening at inlet 56 when rotor 100 is positioned in pumpchamber 58. This allows more molten metal to enter pump chamber 58 forgiven time period thus enabling rotor 100 and pump 10 to move moremolten metal per rotor revolution. Because pump 10 including rotor 100can pump more metal per revolution of rotor 100, pump 10 can, ifdesired, be operated at lower speeds. This decreases vibration and leadsto longer life of the pump components. Therefore, if operated at a lowerspeed, pump 10 can achieve the same results as other molten metal pumpswhile requiring less maintenance, which saves money in parts, labor andreduced down time. Alternatively, pump 10 can be operated at the samespeed as molten metal pumps utilizing conventional rotors, in which caseit will generate a greater flow than such molten metal pumps. Thecut-away portion 134A helps to allow even more molten metal into thepump than previous designs.

As shown, each vane 102 has a circumferential length L and the recess isat least 50% L and is preferably at least ⅔ L. The cut-away portion 134Apreferably reduces the length L by 10-25 percent of what it would be ifthe angled surface 134 continued without interruption to base 108 ofrotor 100.

Having thus described some embodiments of the invention, othervariations and embodiments that do not depart from the spirit of theinvention will become apparent to those skilled in the art. The scope ofthe present invention is thus not limited to any particular embodiment,but is instead set forth in the appended claims and the legalequivalents thereof. Unless expressly stated in the written descriptionor claims, the steps of any method recited in the claims may beperformed in any order capable of yielding the desired result.

1. A pump for pumping molten metal, the device comprising: (a) asuperstructure; (b) a motor positioned on the superstructure; (c) adrive shaft having a first end and a second end, the first end beingconnected to the motor; (d) a pump base having an input port, a pumpchamber, a chamber wall and a discharge leading to an output port; and(e) a rotor connected to the second end of the drive shaft, the rotorpositioned in said pump chamber and having a vane including: (i) a firstsurface for moving molten metal into the pump chamber, the first surfacehaving a downwardly-curved, leading portion; and (ii) a second surfacefor moving molten metal towards the chamber wall, the second surfacebeing positioned farther from the inlet than the first surface andhaving a downwardly sloping portion.
 2. The pump of claim 1 wherein thepump base includes a top surface and the output port is in the topsurface, the device further including a metal-transfer conduit extendingfrom said output port to the superstructure, and a clamp on thesuperstructure for securing the metal-transfer conduit.
 3. The pump ofclaim 1 wherein the pump base includes a side surface and the outputport is in the side surface, the device further including a gas-releasedevice for releasing gas into a stream of molten metal generated by thedevice.
 4. The pump of claim 3 wherein the gas-release device isconnected to the discharge for the release of gas therein.
 5. The pumpof claim 3 which further includes a metal-transfer conduit extendingfrom the discharge, the gas-release device being connected to themetal-transfer conduit for the release of gas therein.
 6. The pump ofclaim 1 which includes a gas-release device for releasing gas directlyinto the pump chamber.
 7. The pump of claim 1 wherein the rotor furtherincludes a top surface and a recess juxtaposed the top surface forallowing molten metal to enter the pump chamber.
 8. The pump of claim 7wherein the recess comprises an angled surface formed next to the topsurface and a vertical surface formed next to the angled surface.
 9. Thepump of claim 7 wherein the vane has a circumferential length and therecess comprises at least 50% of the length.
 10. The pump of claim 9wherein the recess comprises at least ⅔ or more of the length.
 11. Thepump of claim 9 wherein the rotor has a base and the vertical surfaceextends to the base.
 12. The pump of claim 1 wherein the rotor includesa horizontally-extending projection, the projection including a leadingedge, a top surface and a bottom surface, the first surface being formedon the bottom surface of the projection.
 13. The pump of claim 12wherein the projection has a width and a height and the second surfacehas a height, the height of the projection being no more than ½ theheight of the second surface.
 14. The pump of claim 12 wherein thesecond surface is the leading face of a vertical portion of the vane,the vertical portion having a width and including a trailing face, arecess being formed on the vane, the recess extending from the topsurface of the projection to the trailing face of the vertical portion.15. The pump of claim 14 wherein the width of the vertical portion is nogreater than ½ the width of the projection.
 16. The pump of claim 14wherein the recess begins on the upper surface at a position forward ofthe second surface.
 17. The pump of claim 8 wherein the angled surfaceis formed at a 30 degree -60 degree angle.
 18. The pump of claim 7wherein the top surface is flush with the inlet.
 19. The pump of claim 1wherein the second surface of the rotor is vertical.
 20. The pump ofclaim 1 wherein the rotor vane is comprised of graphite.
 21. The pump ofclaim 1 wherein the rotor is imperforate.
 22. The pump of claim 1wherein the rotor is imperforate wherein the rotor includes three vanes.23. The pump of claim 1 that is a circulation pump.
 24. A dual-flowrotor for directing molten metal into and out of a pump chamber, therotor including a rotor vane comprising: (a) a first means for movingmolten metal into the pump chamber; and (b) a second means for movingmolten metal towards the chamber wall.
 25. The rotor of claim 24wherein: (a) the first means for moving molten metal into the pumpchamber is a downwardly-curved surface on the leading portion of thevane; and (b) the second means for moving molten metal towards thechamber wall is a second surface beneath said curved surface.
 26. Therotor of claim 25 wherein said second surface has a downwardly slopingportion.
 27. The rotor of claim 24 wherein the vane further comprises atop surface and a recess means adjacent the top surface to allow moltenmetal to enter a pump chamber.
 28. The rotor of claim 27 wherein therotor further comprises multiple vanes and a recess between each of thevanes.